Inventive concepts relates to semiconductor memories, and more particularly, to an operation method of a nonvolatile memory device.
A semiconductor memory device is implemented using a semiconductor such as silicon Si, germanium Ge, gallium arsenide GaAs, indium phosphide InP, etc. A semiconductor memory device may be classified as a volatile memory device or a nonvolatile memory device.
A volatile memory device loses may loses stored data when a power supply is interrupted. A nonvolatile memory device may retain stored data even when a power supply is interrupted. Examples of the volatile memory device include a SRAM (Static RAM), a DRAM (Dynamic RAM), a SDRAM (Synchronous DRAM), etc. Examples of the nonvolatile memory device are a read only memory (ROM), a programmable ROM (PROM), an electrically programmable ROM (EPROM), an electrically erasable and programmable ROM (EEPROM), a flash memory device, a phase change RAM (PRAM), a magnetic RAM (MRAM), a resistive RAM (RRAM), a ferroelectric RAM (FRAM), etc.
A flash memory may include charge trap flash (CTF) memory cells. The charge trap flash (CTF) memory cell may remember a program state by storing charges in a charge storage layer. Charges stored in the charge storage layer of the charge trap flash (CTF) memory cells are programmed and then flow into a channel. As charges flow into the channel, a distribution of threshold voltages of the charge trap flash (CTF) memory cells may be changed. Because of a physical characteristic of the charge trap flash (CTF) memory cells, reliability of data stored in the memory cells may be degraded.